With the development of flat panel display technologies, it has become a trend in developing flat display panels with high resolution, high contrast, high refresh rate, narrow bezel, and small thickness. At present, liquid crystal panels are still mainstream products of flat panel display technologies. In order to realize narrow bezel, small thickness, and low cost of liquid crystal display panels, GOA technology is greatly developed and has been well used.
FIG. 1 schematically shows a GOA circuit. The GOA circuit comprises a pull-up control module A, a pull-up module B, a pull-down module C, a first pull-down holding module D1, and a second pull-down holding module D2. When point G(n−3) is at a high level, point Q(n) is charged and pulled high, at which time T21 is turned on, and a high level of CLK pulls point G(n) high and outputs a high-level scanning signal. When point G(n+3) is at a high level, the pull-down module pulls the point G(n) and the point Q(n) down simultaneously, and operating points of the pull-down holding module are the low level of G(n) and a high level of point LC1 (or LC2). A GOA control timing diagram is as shown in FIG. 2. LC1 and LC2 are low-frequency signals having periods twice a frame period and having ½ duty cycles, and a phase difference between LC1 and LC2 is ½ period. Control signals needed by the GOA circuit in operation include clock signals, synchronous trigger signals, low-frequency pull-down holding control signals, and VSS low-voltage signals.
A GOA circuit is formed by a plurality of field-effect thin film transistors (TFT). Voltages at operating points of TFTs are closely related to operating environment. Panels are usually operated at normal temperature environment (about 25° C.). Because of heat produced by the circuit in operation, temperature inside a panel can reach above 40° C., and temperature of a GOA area can reach up to above 70° C. Temperature of a working environment of a panel can be as low as −50° C. considering that the panel may be used in severely cold areas. A working temperature of a GOA circuit can therefore actually range from −60° C. to 80° C. In order to satisfy a certain temperature scope of the working environment, a cut-in voltage of a GOA circuit is purposely increased to above 30 V when a driving circuit is designed. It is known from a reliability test of a GOA circuit that when temperature is increased, a TFT in the GOA circuit needs a higher working voltage, while when temperature is decreased, the TFT in the GOA circuit needs a lower cut-in voltage. Voltage at an operating point of a TFT can directly affect service life of the TFT. If the TFT uses a high working voltage at high temperature, the TFT will decay quickly. If the working voltage of the TFT is not increased at low temperature, normal output of gate scanning signal will be affected, which can reduce charging rate.
FIG. 3 shows a driving circuit of a GOA liquid crystal panel. The circuit comprises a power integrated circuit (power IC), a timing control circuit (Tcon circuit), a gamma module, and a source integrated circuit (source IC). The power IC is configured to supply a voltage source to each driving module and a panel. The Tcon circuit is configured to provide control signals for the source IC and a GOA circuit of the panel in operation. The gamma module is configured to provide a reference voltage which is needed by the source IC during digital-to-analogue conversion. The source IC is mainly configured to convert digital gray scale signals to liquid crystal voltages which are applied on two sides of liquid crystals. Control signals provided by the Tcon circuit include starting signal (STV)/clock signal (CLK)/low-frequency clock driving signal (LC). High and low levels of these signals are usually fixed values. A high level of the CLK is a high level outputted by the GOA circuit, and DC low voltage (VSS) is a low level outputted by the GOA circuit.